In recent years, digital terrestrial broadcasting in the UHF (Ultra High Frequency) band is being carried out. The physical channels of digital terrestrial broadcasting are divided into plural segments (13 segments for digital terrestrial broadcasting in Japan). Of these, broadcasting intended for mobile terminals (hereinafter called 1seg) is conducted in the band for one segment. Additionally, broadcasting intended for stationary terminals such as television receivers, etc. is conducted in the bands for the remaining 12 segments (see PTL 1, for example).
With digital terrestrial broadcasting, in practice there exist many empty channels other than the channels over which digital terrestrial broadcasting is conducted in respective regions among the channels 13 to 52 in the UHF band. For this reason, methods of effectively utilizing such empty channels are being investigated.
One promising method that effectively utilizes empty channels is a method that conducts multi-channel community broadcasting over empty channels. Herein, multi-channel community broadcasting is broadcasting in one-segment units multilaterally conducted by utilizing a plurality of logical channels in a limited region. The one segment referred to herein is of a plurally divided band for a single digital terrestrial broadcasting channel. Hereinafter, multi-channel community broadcasting will be simply referred to as community broadcasting.
Meanwhile, with digital terrestrial broadcasting intended for stationary terminals, it is possible to apply reception restrictions by using a CAS (Conditional Access System) format. Meanwhile, although a CAS format is not being used for 1seg broadcasting, it is anticipated that a CAS format similar to that of broadcasting intended for stationary terminals will be adopted in the case where reception restrictions become necessary. Thus, hereinafter, such a case will be explained.
FIG. 1 is a diagram explaining a CAS format for 1seg broadcasting.
NIT is a table containing information regarding frequency information for individual broadcasting services in order to tune the carrier upon which specific broadcasting services are transmitted, and corresponding services. More specifically, as illustrated in FIG. 1, a reception-restricted 1seg broadcasting NIT (Network Information Table) is composed of the network ID (NID) for the 1seg broadcasting, tuning information indicating the frequency, and a service list of broadcasting services, etc. Herein, the network ID is an ID unique to the network. The service list is composed of a service ID (ServiceID) and a service type (ServiceType) for a broadcasting service, etc. The service ID is an ID unique to a broadcasting service, while the service type is the type of broadcasting service (television broadcast, radio broadcast, etc.).
A receiving terminal that receives 1seg broadcasting acquires a service ID from this NIT, and acquires a PMT (Program Map Table) corresponding to that service ID. Herein, a PMT is information that manages the content constituting a broadcasting service. More specifically, as illustrated in FIG. 1, a PMT is composed of a service ID, a PCR_PID, ES information on ESs (Elementary Streams) constituting the broadcasting service for 1seg broadcasting corresponding to that service ID, and 1seg CAS information, which is CAS information for that broadcasting service, etc.
The PCR_PID is an ID unique to a PCR (Program Clock Reference) packet (hereinafter called a packet ID). Also, ES information (Elementary stream information) is composed of an ES_PID, which is the packet ID for an ES (Elementary stream), and an ES_type, which is the type of the ES, etc. 1seg CAS information is composed of a CAS format and an ECM_PID, which is the packet ID for ECM (Entitlement Control Message) packet, etc. An ECM packet is a packet of information shared by all users and including an encrypted scramble key as information related to the scramble key used by that CAS format. Herein, a key for decrypting the encrypted scramble key is included in an EMM (Entitlement Management Message) packet, which is a packet of information individual to each user.
EMM packets are encrypted and included in a digital terrestrial broadcast. An EMM packet can be acquired by decrypting using a key included in an IC (Integrated Circuit) card, etc. issued as a result of the user of a receiving terminal conducting registration for receiving reception-restricted broadcasting (hereinafter called reception registration).
Consequently, the user of a receiving terminal first conducts reception registration and acquires an IC card, etc. that includes a key for unlocking the encryption on an EMM packet. Then, the user uses that IC card to cause the receiving terminal to acquire an EMM packet. The receiving terminal unlocks the scrambling of the encrypted scramble key included in an ECM with the key included in that EMM packet. Using the scramble key obtained as a result, the scrambling of the 1seg broadcasting ESs corresponding to ES information included in a PMT is unlocked. As a result, the video and audio of reception-restricted 1seg broadcasting can be played back.